1. Field of Invention
The present invention relates to technologies for displaying images using electro-optical elements, such as organic light-emitting diode (hereinafter, referred to as an OLED) elements.
2. Description of Related Art
Active-matrix devices including thin-film transistors provided for respective pixels in order to control currents supplied to electro-optical elements have been suggested as electro-optical devices for displaying images using electro-optical elements. However, devices of this type have a problem of display unevenness caused by variation in characteristics (for example, a threshold voltage) of the thin-film transistors.
In order to solve the problem, for example, patent document 1 discloses a pixel circuit shown in FIG. 16. As shown in FIG. 16, in a pixel circuit 8, a driving transistor 82 and a lighting control transistor 83 are arranged in a path from a power line 80 to which a high-potential voltage Vdd of a power supply is applied to an OLED element 81. The driving transistor 82 controls a current Ic (hereinafter, referred to as a “driving current Ic”) supplied to the OLED element 81, and the lighting control transistor 83 controls a period during which the OLED element 81 emits light. The pixel circuit 8 also includes a transistor 85 for diode-connecting the gate and the drain of the driving transistor 82, a transistor 87 arranged in a path from the driving transistor 82 to a constant-current source 86, and a capacitor 88 whose one end is connected to the gate of the driving transistor 82. With this arrangement, first, the transistor 85 that is turned on due to application of a voltage VP causes the driving transistor 82 to be diode-connected, and a current Idata (hereinafter, referred to as a “data current Idata”) corresponding to a desired gray level flows in a path from the power line 80 to the constant-current source 86 via the driving transistor 82 and the turned-on transistor 87. Here, the gate voltage of the driving transistor 82 corresponding to the data current Idata is held in the capacitor 88. Second, the lighting control transistor 83 is turned on due to application of a voltage VR when the transistors 85 and 87 are turned off, and the driving current Ic corresponding to the voltage held immediately before in the capacitor 88 flows into the OLED element 81 via the driving transistor 82 and the lighting control transistor 83.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2003-22049 (see FIG. 17)